Combustion engines such as gas turbine engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor.
A variety of combustor designs exist, with different designs being selected for suitability with a given engine and to achieve desired performance characteristics. One popular combustor design includes a centralized pilot burner (hereinafter referred to as a pilot burner or simply pilot) and several main fuel/air mixing apparatuses, generally referred to in the art as injector nozzles, swirlers, main swirlers or main swirler assemblies, arranged circumferentially around the pilot burner. With this design, a central pilot flame zone and a mixing region are formed. During operation, the pilot burner selectively produces a stable flame that is anchored in the pilot flame zone, while the fuel/air mixing apparatuses produce a mixed stream of fuel and air in the above-referenced mixing region. The stream of mixed fuel and air flows out of the mixing region, past the pilot flame zone, and into a main combustion zone of a combustion chamber, where additional combustion occurs. Energy released during combustion is captured by the downstream components to produce electricity or otherwise do work.
It is known that high frequency pressure oscillations may be generated from the coupling between heat release from the combustion process and the acoustics of the combustion chamber. If these pressure oscillations, which are sometimes referred to as combustion dynamics, or as high frequency dynamics (“HFD”), reach a certain amplitude they may cause nearby structures to vibrate and ultimately break. A particularly undesired situation is when a combustion-generated acoustic wave has a frequency at or near the natural frequency of a component of the gas turbine engine. Such adverse synchronicity may result in sympathetic vibration and ultimate breakage or other failure of such component.
Various resonator boxes for the combustion section of a gas turbine engine have been developed to damp such undesired acoustics and reduce the risk of the above-noted problems. For example, U.S. Pat. No. 5,373,695, issued Dec. 20, 1994 to Aigner et al., teaches a “scavenged” Helmholtz resonator, consisting of a supply tube, resonance volume and damping tube, in the region of the burners. FIG. 1 of this patent shows the resonator aligned with, and not downstream of, premixing burners at the inlet end of the combustion chamber.
U.S. Pat. No. 5,644,918, issued Jul. 8, 1997 to Gulati et al. teaches forming one or more resonance cavities for Helmholtz resonators between first and second plates located in the head end of the combustor casing. These plates define a space that includes the main fuel/air mixing apparatuses, which are referred to as premixers. No pilot burner is included in this design. This patent also teaches providing a cavity between the casing and the liner, so as to form one or more Helmholtz resonators circumferentially about a portion of the combustor.
U.S. Pat. No. 7,089,741, issued Aug. 15, 2006 to Ikeda et al. teaches forming a resonance space about a wall of a combustion liner that defines a combustion region. The resonance space connects to the combustion region by a plurality of through-holes. Additionally, cooling holes are provided along the sides of housings that help define the resonance space, stated as desirable along an upstream side and also shown along a downstream side. Purge holes also are provided along a more radially outwardly disposed surface.
While the above approaches may provide one or more favorable features, to address undesired combustion-generated acoustic waves there still remains in the art a need for a more effective and efficient resonator.